说明：  nc 和psnr的计算代码，直接接入参数即可进行计算，是图像处理尤其是去噪、水印、复原测试效果的时候必须用到的函数
(The calculation codes of NC and PSNR can be calculated by directly accessing parameters, which are necessary functions for image processing, especially for denoising, watermarking and restoration test results)